Laminated film for optical use

ABSTRACT

There is provided a laminated film for optical use comprising a polyester film which has a lubricity layer containing globular particles in at least one side thereof, wherein the laminated film has a thickness irregularity of 0.5 to 7.0%, and wherein the polyester film contains inert particles derived from catalysts and the amount of the inert particles determined by a dark-field microscopy satisfies the following conditions:
         the number of inert particles having a particle size of from 1 to 10 μm is 200 to 20,000/mm 2 ; and   the number of inert particles having a particle size of greater than 10 μm is 10/mm 2  or less.       

     The laminated film for optical use which is improved in uniformity, transparency, lubricity, color tone and scratch resistance, which deposits only a reduced amount of low molecular materials, and which is excellent in the adhesion to a layer adopted for various optical purposes.

TECHNICAL FIELD

This invention relates to a laminated film for optical use. Moreparticularly, the invention relates to a laminated film for optical usewhich is suitably used as a base material for reflection preventivefilms, touch screens, diffusion plates and so on for display devicessuch as LCDs, CRTs, PDPs and ELs.

BACKGROUND ART

A polyester film is excellent in strength, dimensional stability andchemical resistance and, therefore, the film is used for opticalpurposes. The polyester film is especially useful for display devicessuch as LCDs, CRTs, PDPs and ELs.

In the field of display devices, images have recently been displayedmore and more precise and reproduced in color. Accordingly, there hasarisen a strong demand for a laminated film for optical use having auniform thickness, transparency, lubricity, and colorlessness of thecolor tone.

A polyester film by itself lacks lubricity and is difficult to behandled. Therefore, inorganic particles such as silica, calciumcarbonate, kaolin etc., or organic particles such as silicone,cross-linked polystyrene, etc., are generally mixed, as lubricants, intothe polyester film to form minute projections on the surface of the filmto improve the lubricity.

To improve the lubricity by this method, however, it is necessary to bemixed with at least several hundreds ppm of inorganic or organicparticles. Due to these particles light is scattered to causedegradation of the transparency of the polyester film. In addition,these particles help to decompose the polyester whereby the polyesterfilm is likely colored yellow.

To maintain the transparency of the polyester film, there have beenproposed to form a lubricity layer on the surface of the polyester filmwithout mixing the inorganic or organic particles into the film, tobalance the transparency and lubricity.

Even by this method, however, it is difficult to uniformly stretch thepolyester film to produce a biaxially stretched polyester film and,thus, it was difficult to obtain a polyester film having a uniformthickness and orientation.

DISCLOSURE OF THE INVENTION

The present invention aims at solving the problems of the above priorarts.

The purpose of the invention is to provide a laminated film for opticaluse which is improved in the uniformity, lubricity, color tone andscratch resistance, which deposits only a reduced amount of lowmolecular materials, and which is excellent in the adhesion to the layeradopted for various optical applications.

According to the invention, the purpose is achieved by providing alaminated film for optical use comprising a polyester film which has alubricity layer containing globular particles in at least one sidethereof, wherein the laminate film has a thickness irregularity of 0.5to 7.0%, and wherein the polyester film contains inert particles derivedfrom catalysts and the amount of the inert particles determined bydark-field microscopy satisfies the following conditions:

the number of inert particles having a particle size of from 1 to 10 μmis 200 to 20,000/mm²; and

the number of inert particles having a particle size of greater than 10μm is 10/mm² or less.

The invention is explained in detail.

<Polyester Film>

The polyester polymer, which constitutes the polyester film, may be anaromatic polyester, preferably polyethylene terephthalate, orpolyethylene-2,6-naphthalene dicarboxylate. The aromatic polyester maybe a homopolymer or a copolymer.

When a copolymer is adopted, there may be used, as the dicarboxylic acidcomponent to be copolymerized, aliphatic dicarboxylic acids such asadipic acid and sebacic acid; aromatic dicarboxylic acids such asterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid;polyfunctional carboxylic acids such as trimellitic acid. As the diolcomponent to be copolymerized, there may be used aliphatic glycols suchas diethylene glycol, triethylene glycol, trimethylene glycol,tetramethylene glycol and neopentyl glycol, etc; cycloaliphatic glycolssuch as 1,4-cyclohexanedimethanol. The polyester film may containanti-static agents and anti-oxidizing agents, for example.

The polyester film is preferably a biaxially oriented film to obtain ahigh mechanical strength.

<Inert Particles>

A polyester polymer is polymerized normally in the presence of metalliccompounds used as catalysts. The metallic compounds remain in a form ofinert particles in the polyester film. Accordingly, inert particlesderived from catalysts are present in the polyester film.

For example, there are added, at the time of an ester exchange reaction,compounds of metals such as manganese, magnesium, calcium, lithium,sodium and potassium, or phosphorous compounds to the polymer material.Further, there are added, at the time of a polycondensation reaction ofthe polyester polymer, compounds of metals such as antimony, germaniumand titanium. During the polycondensation reaction of the polyesterpolymer, these metallic compounds react with the dicarboxylic acidcomponent or the diol component each of which is a constitutingcomponent of the polyester polymer, and form inert particles in whichthe metallic components bond solely or compositely to the organiccomponents.

When the metallic components bond to the dicarboxylic acid component orto the diol component, which constitutes the polyester polymer, theresulting inert particles have a refractive index different from that ofthe polyester film.

The size and amount of the inert particles can be controlled by properlyselecting the type, amount and the combination of the metalliccompounds, and the temperature and reaction speed of synthesizing thepolyester polymer.

The polyester polymer may contain, in addition to the inert particles,other minute, inorganic and inactive particles and organic inactiveparticles having an average particle size of 2 μm or less if theiramount is extremely small, such as from 3 to 50 ppm. Examples of theinorganic inactive particles include silica, kaolin, alumina, calciumphosphate and those of organic inactive particles include globularcross-linking polyacryl, globular cross-linking polystyrene and globularsilicone.

According to the laminated film of the invention, the laminated filmrecovered in the production stage can be re-used as the startingmaterial. In this instance, the laminated film having a lubricity layercontaining globular particles is melted and chipped to be used as therecovered polymer. The recovered polymer is mixed with a newlypolycondensated virgin polymer. Thus, the resulted polyester filmcontains a small amount of the globular particles which are same asthose contained in the lubricity layer. This embodiment also is includedin the invention.

The amount of the inert particles derived from the catalysts containedin the polyester film can be determined by a dark-field microscopy,details of which are explained later in the column of Examples. In thedetermination, a very small amount of inorganic inactive particles andorganic inactive particles may be seen simultaneously. However, theseparticles also are treated and measured as inert particles derived fromcatalysts because their amount is very small according to the invention.

With respect to the amount of the inert particles derived from thecatalysts, the particles having a particle size of 1 to 10 μm arepresent in an amount of 200 to 20,000/mm², preferably 300 to 15,000/mm²,and more preferably 500 to 10,000/mm². When the amount is less than200/mm², the film is likely stretched ununiformly when it is biaxiallystretched because of the shortage of the stress concentration preventiveeffect and of other reasons, causing uneven thickness, irregularorientation, etc. When the amount is more than 20,000/mm², thetransparency of the film is degraded due to scattering of light by toomany particles, resulting in the problem of blurring images when theresultant film is used for optical purposes.

The amount of the inert particles derived from the catalysts iscontrolled such that the number of particles having a particle size ofover 10 μm is 10 particles/mm² or less. When there are more than 10particles/mm², foreign matter defects appear on the image when theproduct is used as a laminated film for optical use.

The polyester film contains preferably no filler in view oftransparency, according to the invention.

<Lubricity Layer>

The laminated film of the invention has a lubricity layer on at leastone surface of the film. The lubricity layer has both the lubricity andadhesion properties.

The lubricity layer is preferably prepared by applying a mixeddispersion of the high molecular binder with the inert particlesconstituting the lubricity layer to a not-yet stretched sheet ormonoaxially stretched film, and stretching and providing an inlinecoating process comprising a heat-treatment to the sheet or film.

The lubricity layer contains globular particles. The lubricity layercontains preferably both the globular particles and the high molecularbinder, wherein the refractive index of the globular particles ispreferred to be substantially same as that of the high molecular binder.The substantially same refractive index means that the difference in therefractive index between the globular particles and the high molecularbinder is 0.02 or less, and preferably 0.1 or less.

<High Molecular Binder>

A high molecular binder is preferably water-soluble orwater-dispersible, but a binder which is soluble in water containing acertain amount of an organic solvent can be also used. A polyester resinis a preferred high molecular binder in view of producing an excellentadhesion, according to the invention. The polyester resin may beemployed alone, but it is preferably used as a mixture with an acrylicresin having oxazoline groups and polyalkylene oxide chains. The highmolecular binder contained in the lubricity layer has a refractive indexin the range preferably between 1.50 and 1.60.

<Polyester Resin>

Polyester obtained from the polybasic acid components and the diolcomponents, selected from those shown below, can be used as thepolyester resin constituting the high molecular binder. Examples of thepolybasic components include terephthalic acid, isophthalic acid,phthalic acid, phthalic anhydride, 2,6-naphthalene dicarboxylic acid,1,4-cyclohexane dicarboxylic acid, adipic acid, sebacic acid,trimellitic acid, pyromellitic acid, dimer acid and 5-sodiumsulfoisophthalic acid. A preferred polyester resin constituting the highmolecular binder is polyester copolymerized with two or moredicarboxylic acids. The polyester resin may contain unsaturatedpolybasic components such as maleic acid and itaconic acid; andhydroxylcarboxylic acid components such as p-hydroxy benzoic acid, iftheir amount is not too great.

Examples of the diol components for the polyester resin include ethyleneglycol, 1,4-butanediol, diethylene glycol, dipropylene glycol,1,6-hexanediol, 1,4-cyclohexane dimethanol, xylene glycol, dimethylolpropane, poly(ethylene oxide)glycol, and poly(tetramethylene oxide)glycol.

The glass transition point of the polyester resin of the high molecularbinder is preferably 40 to 100° C., and more preferably 60 to 80° C. Thefilm obtained from the polyester resin of the above range showsexcellent adhesion and scratch resistance. When the glass transitionpoint is less than 40° C., a blocking action likely occurs betweenfilms, while when the point is over 100° C., the coating film ishardened to become brittle, degrading the scratch resistance, which isnot preferable.

The intrinsic viscosity of the polyester resin of the high molecularbinder is preferably 0.4 or more and less than 0.7, and more preferably0.5 or more and less than 0.7. Within this range, the production of lowmolecular materials from the polyester resin can be suppressed. Further,excellent adhesion and scratch resistance can be obtained because thepolyester resin has high cohesion strength. When the intrinsic viscosityis less than 0.4, low molecular materials are produced from thepolyester resin, causing degrading the transparency of the basematerial, which is not preferable.

The polyester resin can be produced by the process shown below forexample. The dicarboxylic acid component and the diol component arecharged into an ester exchange reactor. A catalyst is added to themixture and an ester exchange reaction is carried out in a nitrogenatmosphere at 230° C., while the produced methanol is distilled off.Then, the temperature is gradually raised to 255° C., and the pressurein the system is reduced for carrying out a polycondensation reaction toobtain a polyester resin. When the molecular weight increases during thepolycondensation, so the melting viscosity is increased, causingdifficulty in stirring the system. The polyester resin used for thelubricity layer has high melting viscosity even though it has a lowmolecular weight, in comparison with homo-polyethylene terephthalate andit is extremely difficult to stir the system. The intrinsic viscositycan be increased by raising the motor torque of the mixer, improving theshape of the impellers, extending the polymerizing time, etc.

The polyester-resin constituting the high molecular binder is containedin the lubricity layer in an amount of preferably 5 to 95 w/t %, morepreferably 50 to 90 w/t %, and still more preferably 60 to 90 w/t %,based-on the weight of the lubricity layer. When the amount is less than5 w/t %, the adhering power to the polyester film is reduced, resultingin insufficient adhesion to a hard coat and adhesive. When the amount ofthe polyester resin is greater than 95 w/t %, the cohesive power of thelubricity layer is reduced, causing an insufficient adhesion to the hardcoat and adhesive, which is not preferable.

<Cross-Linker>

The lubricity layer preferably contains a cross-linker. The cross-linkeris preferably mixed as a component for constituting the high molecularbinder of the lubricity layer. Preferred examples of the cross-linkerinclude epoxy, oxazoline, melamine and isocyanate. From among them,oxazoline is preferred from the point of ease of handling and the potlife of the coating solution. The most preferred embodiment of mixingthe cross-linker includes using an acrylic resin as a high molecularbinder, and using the cross-linker as the component for constituting theacrylic resin.

Examples of the cross-linger include poly-epoxy compounds, di-epoxycompounds, mono-epoxy compounds and glycidyl amine compounds. Examplesof the poly-epoxy compounds include sorbitol, polyglycidylether,polyglycerol polyglycidylether, pentaerythritol polyglycidylether,diglycerol polyglycidylether, triglycidyltris (2-hydroxyethyl)isocyanate, glycerol polyglycidylether, and trimethylol propanepolyglycidylether. Examples of the di-epoxy compounds includeneopentylglycol glycidylether, 1,6-hexanediol diglycidylether,resorcindiglycidylether, ethylene glycol diglycidylether,polyethyleneglycol diglycidylether, propyleneglycol diglycidylether,polypropylene glycol diglycidylether, and polytetramethyleneglycoldiglycidylether. Examples of monoepoxy compounds includeallylglycidylether, 2-ethylhexylglycidylether and phenylglycidylether.Examples of glycidyl amine compounds includeN,N,N′,N′-tetraglycidyl-m-xylylenediamine, and1,3-bis(N,N-diglycidylamino)cyclohexane.

As the cross-linker, oxazoline is most preferable. Particularly, it ispreferred to use the oxazoline in a form of a polymer containingoxazoline groups. Such a polymer can be obtained by polymerizing solelyan additive-polymerization type, oxazoline group containing monomer, orwith other monomer.

Examples of the additive-polymerization type, oxazoline group containingmonomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline,2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline,2-isopropenyl-4-methyl-2-oxazoline, and2-isopropenyl-5-ethyl-2-oxazoline. These compounds may be used eithersingly or in a form of a mixture. Among them, 2-isopropenyl-2-oxazolineis easily available in trade and is suitably used.

As other monomers which are copolymerizable with theadditive-polymerization type, oxazoline group-containing monomer can beused. Examples of the other monomers include (meth) acrylates such asalkyl acrylate, alkyl methacrylate (the alkyl group may be, for example,methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl,2-ethylhexyl or cyclohexyl); unsaturated carboxylic acids such asacrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaricacid, crotonic acid styrene sulfonic acid and their salts (for example,sodium salt, potassium salt, ammonium salt and tertiary amine salt);unsaturated nitriles such as acrylonitrile and methacrylonitrile;unsaturated amides such as acrylamide, methacrylamide,N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, andN,N-dialkylmethacrylate(the alkyl group may be, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl orcyclohexyl); vinyl ethers in which polyalkylene oxide is added to theester part of vinyl acetate, vinyl propionate, acrylic acid ormethacrylic acid; α-olefin such as ethylene and propylene;halogen-containing α, β-unsaturated polymers such as vinyl chloride,vinylidene chloride and vinyl fluoride; and α, β-unsaturated aromaticmonomers such as styrene and α-methylstyrene. These monomers may be usedeither singly or in a form of a mixture.

As the melamine cross-linker, preferred are ether compounds obtained byreacting lower alcohols such as methyl alcohol, ethyl alcohol orisopropyl alcohol with methylol melamine derivates which, in turn, areobtained by condensing melamine with formaldehyde, or mixture of theether compounds.

Examples of the methylol melamine derivative include monomethylolmelamine, dimethylolmelamine, trimethylol melamine, tetramethylolmelamine, pentamethylol melamine and hexamethylol melamine.

Examples of the isocyanate cross-linker include tolylene diisocyanate,diphenylmethane-4,4′-diisocyaante, meta-xylylene diisocyanate,hexamethylene-1,6-diisocyanate, 1,6-diisocyanate hexane, an adduct oftolylene diisocyanate with hexane diol, polyol modifieddiphenylmethane-4,4′-diisocyante, carbodiimide modifieddiphenylmethane-4,4′-diisocyante, isophoronediisocyanate,1,5-naphthalene diisocyanate,3,3′-bitolylene-4,4′-diisocyanate,3,3′-dimethyldiphenylmethane-4,4′-diisocyante, and metaphenylenediisocyanate.

The cross-linker may be contained in an amount of preferably 0.1 to 30w/t %, and more preferably 10 to 25 w/t %, based on 100 w/t % of thecomposition of the lubricity layer. When the amount is less than 0.1 w/t%, the cohesive force of the coating film may not be exhibited, causingshortage of the adhesion, which is not preferable. When the amount isover 30 w/t %, the coating film may become extremely hardened, resultingin that the stress relief is reduced and no sufficient adhesion isexhibited, or foreign matters derived from cross-linkers may be producedwhen coated films are recovered to be re-used, which are not preferable.

<Acrylic Resin>

In the case where oxazoline is adopted as the cross-liker, it is mostpreferable to use an acrylic resin which has oxazoline groups andpolyalkylene oxide chains. As the acrylic resin, there may be listed theacrylic resin which uses the following monomer having the oxazolinegroups and the monomer having the polyalkylene oxide chains.

Examples of the monomer having the oxazoline groups include2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline,2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline,2-isopropenyl-4-methyl-2-oxazoline, and2-isopropenyl-5-ethyl-2-oxazoline. These compounds may be used eithersingly or in a form of a mixture. Among them, 2-isopropenyl-2-oxazolineis easily available in trade and is suitably used. By using the acrylicresin having oxazoline groups, the cohesive strength of the lubricitylayer is improved whereby the adhesion to a hard coat, adhesive layer,etc., is strengthened. Further, the use of the acrylic resin havingoxazoline groups gives frictional resistance to metallic rollers used inthe film-producing step, and in the hard coat processing step.

Examples of the monomer having polyalkylene oxide chains may be those inwhich polyalkylene oxide is added to the ester part of an acrylic acidor methacrylic acid. Examples of the polyalkylene oxide chains includepolymethylene oxide, polyethylene oxide, polypropylene oxide andpolybutylene oxide. The number of repeating units of the polyalkyleneoxide chain is preferably 3 to 100. By using the acrylic resin which haspolyalkylene oxide chains, the compatibility between the polyester resinand the acrylic resin of the high molecular binder in the lubricitylayer is improved in comparison with the case where an acrylic resincontaining no polyalkylene oxide chain is used and, accordingly, thetransparency of the lubricity layer can be improved. When the number ofrepeating units of the polyalkylene oxide chain is less than 3, thecompatibility between the polyester resin and the acrylic resin isreduced, causing degradation in the transparency of the lubricity layer,while when number of the repeating units is greater than 100, theresistance to moisture and to heat of the lubricity layer is reduced,resulting in decreasing the adhesion to the hard coat, etc., in a highmoisture and high temperature conditions.

Other monomers, shown below; may be copolymerized with the acrylicresin. Examples of the copolymerizable monomers include alkylacrylateand alkylmethacrylate (the alkyl group maybe, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl orcyclohexyl); hydroxyl-containing monomers such as 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate and2-hydropropylmethacrylate; epoxy group-containing monomers such asglycidyl acrylate, glycidyl methacrylate, and allylglycidyl ether;monomers containing carboxyl groups and their salts such as acrylicacid, methacrylic acid, itaconic acid, maleic acid, fumaric acid,crotonic acid, styrene sulfonic acid and their salts (sodium salts,potassium salts, ammonium salts, tertiary amine salts, etc.); monomershaving amide groups such as acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacryl amide, N,N-dialkylacrylamide,N,N-dialkylmethacrylate (the alkyl group may be, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl orcyclohexyl), N-alkoxyacryl amide, N-alkoxymethacryl amide,N,N-dialkoxyacryl amide, N,N-dialkoxymethacryl amide (the alkoxy groupmay be methoxy, ethoxy, butoxy, isobutoky, etc.), acryloyl morpholine,N-methylol acrylamide, N-methylol methacrylamide, N-phenyl acrylamideand N-phenyl methacrylamide; monomers of acid anhydrides such as maleicanhydride and itaconic anhydride; vinyl isocyanate, allylisocyanate,styrene, α-methyl styrene, vinylmethyl ether, vinylethyl ether,vinyltrialkoxy silane, alkylmaleic acid monoester, alkyl fumaric acidmonoester, alkyl itaconic acid monoester, acrylonitrile,methacrylonitrile, vinylidene chloride, ethylene, propylene, vinylchloride, vinyl acetate and butadiene.

The acrylic resin which has oxazoline groups and polyalkylene oxidechains, of the high molecular binder, is contained in the lubricitylayer in an amount of preferably 5 to 95 w/t %, more preferably 5 to 90w/t %, and still more preferably 10 to 50 w/t %. When the amount of theacrylic resin having oxazoline groups and polyalkylene oxide chains isless than 5 w/t %, the cohesive power of the lubricity layer isdecreased, causing insufficient adhesion to the hard coat, adhesive,etc. When the amount is greater than 95 w/t %, the adherence to thepolyester film is reduced, resulting in insufficient adhesion to thehard coat, to the adhesive, etc., which is not preferable.

<Globular Particles>

Examples of the globular particles constituting the lubricity layeraccording to the invention include inorganic inert particles of calciumcarbonate, magnesium carbonate, calcium oxide, zinc oxide, magnesiumoxide, silicon oxide, silicate of soda, aluminum hydroxide, iron oxide,zirconium oxide, barium sulfate, titanium oxide, tin oxide, antimonytrioxide, carbon black, molybdenum disulfide, etc.; and organic inertparticles of acrylic cross-linking polymer, styrene-type cross-linkingpolymer, silicone resin, fluorine resin, benzoguanamine resin, phenolicresin, nylon resin, etc. These inorganic or organic particles may beused either singly or in a form of a mixture of two or more kinds.

Preferred globular particles constituting the lubricity layer of theinvention are composite inorganic particles of silica and titania. Thecomposite inorganic particles are suitable because the refractive indexcan be optionally and easily controlled. As the refractive index of thehigh molecular binder is in the range between 1.50 and 1.60, the indexof the globular particles can be easily adjusted to that of the highmolecular binder.

According to the invention, the difference in the refractive index ofthe high molecular binder and that of the globular particles ispreferably within 0.02, and more preferably within 0.01. When thedifference is over 0.02, light scatters greatly due to the difference inthe refractive indexes at the border between the high molecular and theglobular particles, resulting in increasing haze to degrade thetransparency. Both the refractive index of the high molecular binder andthat of the globular particles are preferably in the range between 1.50and 1.60.

The average particle size of the globular particles is preferably 20 to200 nm, and more preferably 40 to 120 nm. When the particle size is lessthan 20 nm, no sufficient lubricity and scratch resistance are obtained.When the average particle size is greater than 200 nm, particles arelikely dropped off, which is not preferable.

The globular particles are contained preferably in an amount of 0.1 to10 w/t % of the lubricity layer. When the amount is less than 0.1 w/t %,no sufficient lubricity and scratch resistance are obtained. When theamount is greater than 10 w/t %, the cohesive force of the coating filmis decreased, resulting in degrading adhesion, which is not preferable.

<Aliphatic Wax>

The lubricity layer preferably contains aliphatic wax. The aliphatic waxis contained preferably in an amount of 0.5 to 30 w/t %, and morepreferably 1 to 10 w/t %, based on the total weight of the lubricitylayer. When the wax is contained in an amount of less than 0.5 w/t %,the film surface may be in short of lubricity, which is not preferable.When the wax is contained in an amount of greater than 30 w/t %, theremay be short of, the adhesion to the polyester film base and, the easyadherence to a hard coat, adhesive, etc. Concrete examples of thealiphatic wax include plant waxes such as carnauba wax, candelilla wax,rice wax, Japanese wax, jojoba oil, palm wax, rosin modified wax,ouricury wax, sugarcane wax, Esparto wax and bark wax; animal waxes suchas bees wax, lanoline, whale wax, Ibotaro, and shellac wax; mineralwaxes such as montan wax, ozokerite and ceresine wax; petroleum waxessuch as paraffin wax, microcrystalline wax and petrolatum wax; andsynthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylenewax, polyethylene oxide wax, polypropylene wax and polypropylene oxidewax. From among these waxes, carnauba wax, paraffin wax and polyethylenewax are particularly preferred in view of the easy adherence to a hardcoat, adhesive, etc. and of the excellent lubricity. These waxes areused preferably in a form of an aqueous dispersion for the decrease ofburdens on the environment and for the ease of handling.

Additives>

The lubricity layer may contain other inert particles to the extent notto affect the transparency, to improve the lubricity and scratchresistance. Examples of the other inert particles include inorganicinert particles of calcium carbonate, magnesium carbonate, calciumoxide, zinc oxide, magnesium oxide, silicon oxide, silicate of soda,aluminum hydroxide, iron oxide, zirconium oxide, barium sulfate,titanium oxide, tin oxide, antimony trioxide, carbon black, molybdenumdisulfide, etc.; and organic inert particles of acrylic cross-linkingpolymer, styrene-type cross-linking polymer, silicone resin, fluorineresin, benzoguanamine resin, phenolic resin, nylon resin, etc. Amongthem, water-insoluble solids are preferably inert particles having aspecific gravity of less than 3, to be prevented from setting out in anaqueous dispersion.

<Dyes and Pigments>

The laminated film of the invention may contain dyes and pigments foradjusting the color tone. The dyes and pigments may be contained ineither the polyester film used as the basic material or the lubricitylayer, or both. Blue-, green- or red-base dyes and pigments may be used.To correct a tinge of yellow of the film, blue-base dyes or pigments canbe effectively used.

Preferred blue-base dyes or pigments include anthraquinone-base bluedyes such as Color Index Solvent Blue 45, and phthalocyanine-base bluepigments having a peak absorption at around 600 to 700 nm. The ColorIndex Solvent Blue 45 is particularly preferred from the point of heatresistance and solubility in polyester.

When dyes or pigments are contained, they may be controlled such thatthe color b*value determined by measuring the permeated light throughthe laminated polyester film is in the range between −0.5 and 1.5.

For example, a blue dye is added to the polyester film preferably in anamount of 0.2 to 5 ppm. When the dye is contained in the lubricitylayer, it is preferably added in an amount of 200 to 5,000 ppm in viewof the thickness of the layer.

<Characteristic Features of the Laminated Film>

The laminated film of the invention has a thickness of preferably 25 to300 μm, more preferably 50 to 250 μm, and still more preferably 100 to250 μm, to have a sufficient strength for supports for liquid crystals,hard coats, touch panels, anti-dazzle treatment goods, electromagneticwave shield film for PDF(plasma display panels), organic ELs (organicelectroluminescence displays), etc.

The thickness irregularity of the film of the invention is 0.5 to 7.0%,preferably 0.7 to 5.0%, more preferably 1.0 to 4.0%. When theirregularity in thickness is less than 0.5%, the film should be producedat an extremely low speed even if it contains inert particles satisfyingthe above conditions. This causes decrease in productivity anddifficulty in commercial production. When the irregularity is greaterthan 7.0%, problems such as distortion of images, color unevenness andso on, may be resulted due to the insufficient uniformity in filmthickness, when the films are used as base materials for reflectionpreventive films, touch screens, diffusion plates, etc.

The haze value of the laminated film of the present invention ispreferably 0.3 to 1.5%. When the value is greater than 1.5%, thesharpness of the images in display devices, etc., is reduced, which isnot preferable.

The average surface roughness (Ra) at the center line of the lubricitylayer surface of the laminated film according to the invention ispreferably 0.002 to 0.01 μm, and the frictional coefficient (μs) of thelubricity layer surface is preferably 0.8 or less. When the lubricitylayer surface has the value in the above range, an excellent lubricityis obtained.

The color b*value determined by measuring the permeated light throughthe laminated film according to the invention is preferably in the rangebetween −0.5 and 1.5. When the value is less than −0.5, the blue colorin images appearing in display devices, etc., tends to be too strong,while when the value is over 15, images tend to become yellow tone, bothof which are not preferable.

Laminated films satisfying these requirements can be obtained by forminglubricity layers composed of the mentioned composition.

<Production Process>

The composition for forming the lubricity layer (referred to sometimesas coating film) is preferably used in a form of an aqueous coatingliquid, such as an aqueous solution, aqueous dispersion or emulsifiedsolution. For forming the coating film, resins other than the abovecomposition may be used when necessary, examples of which includeanti-static agents, coloring agents, surfactants, ultraviolet rayabsorber, cross-linkers, etc.

The concentration of solids in the aqueous coating liquid is normally 20w/t % or less, and preferably 1 to 10 w/t %. When the concentration isless than 1 w/t %, the coating liquid may be short of wetting propertiesto be applied to the polyester film. When the concentration is greaterthan 20 w/t %, the stability of the coating liquid or the appearance ofthe lubricity layer may be degraded, which is not preferable.

The polyester film can be produced, for example, by the followingprocess.

Polyester, for example, is melted and extruded in a film-like form. Theextruded polyester is cooled to be solidified in a casting drum to forma not-yet-stretched film. The not-yet-stretched film is stretched to alongitudinal direction at a temperature of Tg˜(Tg+60)° C. once, twice ormore times so that the film may be enlarged by 3- to 6-foldmagnification. Subsequently, the film is stretched to a cross directionat Tg˜(Tg+60)° C. so that the film may be enlarged by 3- to 5-foldmagnification. When necessary, the film is provided with a furtherthermal treatment at 180 to 230° C. for 1 to 60 seconds, followed by asecond thermal treatment at a temperature lower than that of the thermaltreatment by 10 to 20° C., to be stretched to a cross direction withbeing contracted by 0 to 20%. The glass transition temperature isabbreviated as Tg.

The aqueous coating liquid may be applied to the polyester film at anoptional stage after the not-yet-stretched film is obtained. Preferably,the liquid is applied during the production process of the polyesterfilm, and more preferably it is applied to the polyester film prior tothe time an oriented crystallization is completed.

The polyester film prior to the completion of the orientedcrystallization include a not-yet-stretched film, a monoaxially orientedfilm wherein the not-et-stretched film is oriented either to lengthwiseor crosswise direction, and a film stretched biaxially to both thelengthwise direction and the crosswise direction at a small extent (abiaxially stretched film prior to the completion of the orientedcrystallization by finally re-stretching the film to lengthwise orcrosswise direction). Particularly it is preferred to coat the aqueouscoating liquid of the above composition onto the not-yet-stretched filmor a mono-axially stretched film, to stretch the coated film lengthwiseand/or crosswise and to heat-fix the stretched film.

When the aqueous coating liquid is coated to the film, the film surfaceis preferably provided with a physical treatment, such as a coronasurface treatment, a flame treatment and a plasma treatment, as apreparatory treatment to improve the coating result. Alternately, asurfactant which is chemically inactive with the composition ispreferably used together with the composition. The surfactantcontributes to accelerate the wetting of the aqueous coating liquid tobe applied to the polyester film and to stabilize the coating liquid.Examples of the surfactant include anionic or nonionic surfactants ofpolyoxyethylene-aliphatic acid ester, sorbitan aliphatic acid ester,glycerine aliphatic acid ester, aliphatic acid metallic soap, alkylsulfate, alkyl sulfonate, and alkyl sulfosuccinate. The surfactant ispreferably contained in an amount of 1 to 10 w/t % in the compositionforming the coating film.

The amount of the coating liquid is preferably controlled such that thethickness of the coating film is in the range between 0.01 and 0.3 μm,and preferably between 0.02 and 0.25 μm. When the coating film is toothin, it lacks adhesive power, while when it is too thick, a blocking oran increase in the haze value occurs.

The coating liquid can be applied by a known method, such as a rollcoating, gravure coating, roll brushing, spray coating, air knifecoating, impregnation, curtain coating, etc. These methods can beadopted either singly or in a form of a combination. The coating filmcan be formed on one side surface only or on both sides of the film.

EXAMPLES

The invention is explained with reference to examples.

In the following examples and comparative examples, all parts are basedon weight unless otherwise defined. The evaluation and determination arecarried out by the following methods.

(1) Determination of Particles in the Film by a Dark-Field Micrography

The surface of the laminated film was treated with methylethyl ketone toremove a lubricity layer, and was taken photographs with a microscope(Nikon Microphoto-FX) by a transmission dark-field determination methodwith 10 calibrations and 100-fold magnification. From the obtainedphotographs, the number of particles having a particle size of 1 to 10μm was counted by an image analyzing device. When particles have nospherical form, the average value of the short diameter and the longdiameter of one particle was treated as the particle size.

(2) Thickness Irregularity of the Laminated Film

The thicknesses of the film to the widthwise direction and to thelengthwise direction were determined under the following conditions, byan electronic micrometer (produced by ANRITSU, Model KG601B). Thethickness r was obtained by dividing the difference between theirmaximum value and the minimum value by the film thickness.

Sample area: lengthwise direction 2 m

-   -   widthwise direction 3 m

Measuring intervals: 30 cm intervals to the lengthwise direction

Measuring speed: 5 mm/sec.

(3) Haze Value

The haze value of the film was measured by a haze measuring device(produced by Nippon Denshoku Kogyo, Model NDH-2000), in accordance withthe procedure described in JIS K7136. The haze value of films wasevaluated by the following standard:

-   ⊚): haze value≦1.0% . . . extremely good film haze-   ◯: 1.0%<haze value≦1.5% . . . good film haze-   X 1.5%<haze value . . . bad film haze.    (4) Color b*Value Determined by Measuring the Permeated Light    Through the Laminated Film

The color b*value of the laminated film was determined by measuring thepermeated light, using a color meter (produced by Nippon Denshoku Kogyo;Model SZ-Σ90), in accordance with the procedure described in JI-Z8722and 8729.

(5) Scratch Resistance

A hard chrome-plated pin having 6 mm diameter was fixed. Films, whichwere cut at 20 cm lengthwise and at 15 mm crosswise, were contacted withthe pin by an angle of 90° and were slid on the pin at a predeterminedspeed of 20 mm/sec, and the scratchs on the surfaces of the films wereevaluated by the criteria below:

-   5: no scratch-   4: 0%<scratched area based on the total area≦10%-   3: 10%<scratched area based on the total area≦25%-   2: 25%<scratched area based on the total area≦50%-   1: 50%<scratched area based on the total area    (6) Average Surface Roughness (Ra) at the Center Line

The average surface roughness was determined by a high precision surfaceroughness tester produced by Kosaka Kenkyu-sho, model SE-3FAT, inaccordance with JIS B0601. A chart was drawn by a radius 2 μm needlewith a 30 mg load, at 200,000-fold magnification and a cut-off of 0.08mm. From the surface roughness curve, the part of length L measuredtoward the center line was taken out, and the center line of the takenout part was set as the X-axis and the axial magnification direction asthe Y-axis. When the roughness curve is represented by Y=f (x), thevalue given by the following formula was shown by an nm unit. Fourmeasurements were made with taking 1.25 mm as a reference length and theaverage value of the four measurements was shown.

Ra = (1/L) ∫₀^(L)f (x) 𝕕x(7) Frictional Coefficient (μs)

A static frictional coefficient (μs) between the coating film formingsurface and the polyethylene terephthalate film (surface having nocoating film) was measured by a slippery measuring device (produced byToyo Tester Sha), in accordance with the procedure described in ASTMD1894-63. The sled plate used is a glass plate and a 1 kg load was used.The lubricity of the film was evaluated by the following criteria:

-   ⊚: frictional coefficient (μs)≦0.5 . . . extremely good lubricity-   ◯: 0.5<frictional coefficient (μs)≦0.8 . . . good lubricity-   X: 0.8<frictional coefficient (μs) . . . bad lubricity    (8) Adhesion    Hard Coat

A hard coat layer of 10 μm thickness, formed on the surface of thepolyester to which a coating surface is formed, was cross cut to form100 pieces of 1 mm² grids. A 24 mm wide cellophane tape (produced byNichiban Sha) was pasted onto the cross cuts and was rapidly peeled offwith a peeling angle of 180°. The surface from which the tape was peeledoff was observed and was evaluated in accordance with the followingcriteria.

-   5: peeled off area is 10% or less . . . extremely good adhesion-   4: peeledoff area is 10% ormore and 20% or less . . . good adhesion-   3: peeled off area is 20% or more and 20% or less . . . relatively    good adhesion-   2: peeled off area is 30% or more and 40% or less . . . insufficient    adhesion-   1: peeled off area is 40% or more . . . extremely insufficient    adhesion    Adhesive (PSA)

20 μm thick adhesive (PSA: Pressure Sensitive Adhesive) layer was formedon the laminate film surface on which a coating film is to be applied.The adhesive layer surface was pasted to a float glass and was retainedfor one day under 65% RH atmosphere. Subsequently the adhesive layer waspeeled off from the glass surface with a peeling angle of 90°, and theresidual state of the adhesive on the glass was observed and evaluatedon the basis of the following criteria.

The adhesive (PSA) used comprises a urethane-containing acrylatecopolymer wherein the acrylic component comprises n-butylacrylate (86mol %) and methacrylate (14 mol %).

-   5: residual adhesive area is less than 10% . . . extremely good    adhesion-   4: residual adhesive area is 10% or more and less than 20% . . .    good adhesion-   3: residual adhesive area is 20% or more and less than 30% . . .    relatively good adhesion-   2: residual adhesive area is 30% or more and less than 40% . . .    insufficient adhesion-   1: residual adhesive area is 40% or more . . . extremely    insufficient adhesion    (9) Blocking Resistance

Two films were overlapped with each other such that the coating filmforming surfaces were contacted to each other, were pressed with apressing force of 0.6 kg/cm², for 17 hours at 60° C. under 80% RH, andwere peeled off. The blocking resistance was evaluated by the peelingforce applied in accordance with the following criteria:

-   ⊚: peeling force<98 mN/5 cm . . . extremely good blocking resistance-   ◯: 98 mN/5 cm≦peeling force<147 mN/5 cm . . . good blocking    resistance-   Δ: 147 mN/5 cm≦peeling force<196 mN/5 cm . . . relatively good    blocking resistance-   X: 196 mN/5 cm≦peeling force . . . bad blocking resistance    (10) Glass Transition Temperature

About 10 mg of sample was sealed in an aluminum pan and was connected toa differential scanning calorimeter (produced by Du Pont; Model:V4.OB2000 Type DSC). The sample was heated from 25° C. to 300° C. at aspeed of 20° C./min, was maintained 5 minutes at 300° C., and was takenout to be transferred on ice to be rapidly cooled. The pan was againconnected to the differential scanning calorimeter and was heated from25° C. at a speed of 20° C./min. to determine the glass transitiontemperature (Tg: ° C.).

(11) Intrinsic Viscosity

The intrinsic viscosity η (dl/g) was determined with an o-chlorophenolsolution at 25° C.

(12) Thickness of the Coating Layer

Films fixed in an embedding resin were cut at their cross-sections by amicrotone, and were dyed in a 2% osmium acid at 60° C. for two hours.Then, the thickness of the coating layer was determined by atransmission electron microscope (produced by Nippon Denshi, ModelJEM2010).

(13) Refractive Index

High Molecular Binder

The coating materials were dried to solid in a plate state at 90° C. andits refractive index was measured by an Abbe refractive meter (D line:589 nm).

Inert Particles

Inert particles, dried to solid at a temperature of 90° C., weresuspended in a number of liquids each having a refractive indexdifferent from each other, and the refractive index of the liquid inwhich the suspension is seen most transparent was measured by an Abberefractive meter (D line: 589 nm).

(14) Heat Resistance

Films were heat-treated at 120° C. for 60 minutes and the variation ofeach of their haze values was measured. The variation was evaluatedbased on the following criteria:

-   ⊚: haze value variation≦1.0% . . . the film has an extremely good    heat resistance-   ◯: 1.0%<haze value variation≦2.5% . . . good heat resistance-   X: 2.5%<haze value variation . . . insufficient heat resistance    -   Variation of the haze value=haze value of the heat-treated        film−(minus) haze value of not-yet heat-treated film        (15) General Evaluation

An evaluation was made by the following criteria:

-   ⊚: The scratch resistance is 5; the surface roughness (Ra) is in the    range between 0.002 and 0.01 μm; the adhesion to both the hard coat    and the adhesive is 3 or more; and the evaluations on the haze,    frictional coefficient and blocking resistance are all ⊚. (General    evaluation: extremely good)-   ◯: The scratch resistance is 4 or greater; the surface roughness    (Ra) is in the range between 0.002 and 0.01 μm; the adhesion to both    the hard coat and the adhesive is 3 or more; and the evaluation on    any of the haze, frictional coefficient and blocking resistance is ◯    and there is neither evaluation of Δ nor X. (General    evaluation:good)-   Δ: The scratch resistance is 3 or greater; the surface roughness    (Ra) is in the range between 0.002 and 0.01 μm; the adhesion to both    the hard coat and the adhesive is 3 or more; and the evaluation on    any of the haze, frictional coefficient and blocking resistance is    Δ, and there is no evaluation of X.    (General Evaluation: Relatively Good)

X: There applies at least one item from that the scratch resistance 2 orless; the surface roughness (Ra) is outside the range between 0.002 and0.01 μm; the adhesion to the hard coat or the adhesive is 2 or less; andthe evaluation on any of the haze, frictional coefficient and blockingresistance is X. (General evaluation: bad)

Example 1

There were prepared polyester for a polyester film, and a coating liquidcomprising a polyester resin, an acrylic resin, globular particles andwetting agents.

Polyester for the Polyester Film:

100 parts of dimethyl terephthalate, 65 parts of ethylene glycol and0.04 parts of manganese acetate tetrahydrate were charged into areactor. The mixture was heated to 240° C. in three hours to carry outan ester exchange reaction. Then, 0.02 parts of orthophosphoric acid and0.02 parts of antimony trioxide were added, followed by raising thetemperature to 290° C. in three hours under a reduced pressure (˜2 mmHg)to carry out a polycondensation reaction, resulting in pellets ofpolyethylene terephthalate having an intrinsic viscosity of 0.65 dl/g.

Coating Liquid:

65 w/t % of the polyester resin shown below, 20 w/t % of an acrylicresin, 10 w/t % of globular particles and 5 w/t % of a wetting agentwere mixed and dispersed to prepare an aqueous coating liquid having aconcentration of 8 w/t % of these materials.

Polyester Resin:

A polyester resin comprising, as acid components, 70 mol % of2,6-naphthalene dicarboxylic acid/25 mol % of isophthalic acid/5 mol %of 5-sodiumsulphoisophthalic acid and, as glycol components, 90 mol % ofethylene glycol/10 mol % of diethylene glycol.

Acrylic Resin:

An acrylic resin comprising 25 mol % of methylmethacrylate/30 mol % of2-isopropenyl-2-oxazoline/10 mol % of polyethyleneoxide methacrylate/35mol % of acrylamide. The acrylic resin contains 30 mol % of2-isopropenyl-2-oxazoline as a cross-linker, in the polymer.

Globular Particles:

Globular cross-linking acrylic particles having an average particle sizeof 100 nm.

Wetting Agent:

Polyoxyethylenelauryl ether.

The pellets of polyethylene terephthalate polymer were dried under areduced pressure for six hours at 140° C. and were supplied to anextruder. In the extruder, the polyester resin was melted and extrudedinto a rotary cooling drum, in a form of a sheet by an electrostaticapplying method, air knife method, etc., to obtain a not-yet stretchedsheet having little thickness irregularity. Subsequently, the obtainedsheet was heated to 100° C. and was stretched to the lengthwisedirection (longitudinal direction) by 3.5-fold to obtain a monoaxiallyoriented film. Then, the coating liquid was coated to both surfaces ofthe monoaxially oriented film by a reverse roller method. The film wasfurther stretched to a crosswise direction (widthwise direction) by3.8-fold in a zone heated to 140° C., followed by a heat treatment in aheat treatment zone of 220° C., to obtain a biaxially oriented laminatedfilm for optical use having a thickness of 125 μm. Each of the lubricitylayers formed on both surfaces of the film has a thickness of 80 nm.Evaluation results are shown in Table 1.

TABLE 1 Particles/mm² Film thickness Size Size irregularity Haze Color1~10 μm over 10 μm (%) (%) B* Ex. 1 6,000 3 3.5 0.6 0.5 Ex. 2 17,000 70.8 0.6 0.7 Ex. 3 400 1 6.5 0.5 0.8 Ex. 4 8,600 5 4.5 1.0 1.0 Ex. 56,200 4 3.3 0.5 0.4 Ex. 6 5,800 3 3.6 0.6 −0.3 Ex. 7 6,100 4 3.4 0.6−0.4 Comp. Ex. 1 22,000 9 0.5 0.1 1.6 Comp. Ex. 2 100 2 7.5 0.4 0.5Comp. Ex. 3 6,100 5 3.1 1.6 1.3 Comp. Ex. 4 45,000 20 1.1 2.6 1.8 Ex. =Example Comp. Ex. = Comparative Example

Example 2

Procedures of Example 1 were repeated except that magnesium acetatetetrahydrate was used in place of manganese acetate tetrahydrate, toobtain a laminated film for optical use. Evaluation results are shown inTable 1.

Example 3

Procedures of Example 1 were repeated except that 0.005 parts oftetrabutoxy titanium was used in place of antimony trioxide, to obtain alaminated film for optical use. Evaluation results are shown in Table 1.

Example 4

Procedures of Example 1 were repeated except that the amount of themelted polyester polymer was changed to obtain a film thickness of 175μm and whereby a laminated film for optical use was obtained. Evaluationresults of the film are shown in Table 1.

Example 5

Procedures of Example 1 were repeated except that globular silica havingan average particle size of 80 nm was used in the coating liquid inplace of globular cross-linking acrylic particles, to obtain a laminatedfilm for optical use. Evaluation results of the film are shown in Table1.

Example 6

Procedures of Example 1 were repeated except that 0.0001 parts ofTerazole Blue RLS, as a blue dye, was added following the addition ofantimony trioxide, and a laminated film for optical use was obtained.Evaluation results of the film are shown in Table 1.

Example 7

Procedures of Example 1 were repeated except that 0.1 parts of TerazoleBlue RLS, as a blue dye, was added to the coating liquid, and alaminated film for optical use was obtained. Evaluation results of thefilm are shown in Table 1.

Comparative Example 1

Procedures of Example 1 were repeated except that the amount of antimonyoxide was 0.10 parts and that trimethyl phosphate was used in place ofthe orthophosphoric acid, and a laminated film for optical use wasobtained. Evaluation results of the film are shown in Table 1.

Comparative Example 2

Procedures of Example 1 were repeated except that the amount of theantimony trioxide was 0.01 parts and that the amount of theorthophosphoric acid was 0.06 parts, whereby a laminated film foroptical use was obtained. Evaluation results of the film are shown inTable 1.

Comparative Example 3

Procedures of Example 1 were repeated except that amorphous silicahaving an average particle size of 130 nm was used in place of globular,cross-linking acrylic particles contained in the coating liquid, and alaminated film for optical use was obtained. Evaluation results of thefilm are shown in Table 1.

Comparative Example 4

Procedures of Example 1 were repeated except that the polyester for thepolyester film was synthesized with an addition of 0.05 parts of calciumcarbonate having an average particle size of 0.6 μm, and a laminatedfilm for optical use was obtained. Evaluation results of the film areshown in Table 1.

The qualities of the films are shown in Table 1 for the Examples 1 to 7and Comparative Examples 1 to 4. Films of the Examples are all excellentin thickness irregularity, haze and color tone, as shown in Table 1.

Examples 8 to 10 and Comparative Examples 5 and 6

Melted polyethylene terephthalate ([η]=0.62 dl/g, Tg=78° C.) wasextruded from a die and was cooled in a cooling drum by a conventionalprocess to form a not-yet stretched film, followed by stretching thefilm to the longitudinal direction by 3.2-fold. Then, an aqueous coatingliquid, shown in Table 3, containing a coating material in aconcentration of 8% was coated by a roll coater to both surfaces of theresulted film (each of coating liquids A1 to A6 contains the compositionshown in Table 2 and a high molecular binder of which refractive indexshown in Table 3).

The coated film was dried at 95° C., stretched by 3.5-fold to acrosswise direction at 125° C., contracted by 3% to the width directionand heat-fixed whereby a laminated film for optical use having athickness of 125 μm was obtained. The thickness of the coating film is0.1 μm. Evaluation results of the film are shown in Table 4.

TABLE 2 Lubricity layer composition (w/t %) Polyester Polyester Part.Part. Part. Part. Add. Wet. Coat. material A1 A2 Acryl A1 A2 A3 A4 A1 A1Coat. liquid A1 67 20 3 5 5 Coat. liquid A2 67 20 3 5 5 Coat. liquid A362 20 3 5 5 5 Coat. liquid A4 67 20 3 5 5 Coat. liquid A5 67 20 3 5 5Coat. = Coating Part. = Inert particles Add. = Additives Wet. = Wettingagents

Components composing the coating liquids A1 to A5 above were prepared asfollows:

Polyester Resin A1:

The polyester resin A1 comprises, as acid components, 63 mol % of2,6-naphthalene dicarboxylic acid/32 mol % of isophthalic acid/5 mol %of 5-sodium sulfoisophthalic acid and, as glycol components, 90 mol % ofethylene glycol/10 mol % of diethylene glycol, with Tg of 76° C. and anaverage molecular weight of 12,000. The polyester A1 was prepared, inaccordance with the procedure shown in Example 1 of Kokai (Jpn.Unexamined Patent Publication) 06-116487, as follows:

42 parts of dimethyl 2,6-sodium dicarboxylate, 17 parts of dimethylisophthalate, 4 parts of dimethyl 5-sodium sulfoisophthalate, 33 partsof ethylene glycol and 2 parts of diethylene glycol were charged into areactor, followed by an addition of 0.05 parts of tetrabutoxy titanium.The mixture was heated to a temperature controlled to 230° C. under anitrogen atmosphere, to carry out an ester exchange reaction whiledistilling off the produced methanol. Then, the reaction system wasgradually heated to 255° C. to carry out a polycondensation reactionunder a reduced pressure of 1 mmHg, whereby polyester A1 was obtained.

Polyester Resin A2:

The polyester resin A2 comprises, as acid components, 95 mol % ofterephthalic acid/5 mol % of 5-sodium sulfoisophthalic acid and, asglycol components, 90 mol % of ethylene glycol/10 mol % of diethyleneglycol, with Tg of 72° C. and an average molecular weight of 13,000. Thepolyester A2 was prepared, in accordance with the procedure shown inExample 1 of Kokai (Jpn. Unexamined Patent Publication) 06-116487, asfollows:

56 parts of dimethyl terephthalate, 5 parts of 5-sodium sulfoisophthalicacid, 36 parts of ethylene glycol and 3 parts of diethylene glycol werecharged into a reactor, followed by an addition of 0.05 parts oftetrabutoxy titanium. The mixture was heated to a temperature controlledto 230° C. under a nitrogen atmosphere, to carry out an ester exchangereaction while distilling off the produced methanol. Subsequently, thetemperature of the reaction system was gradually elevated to 255° C. tocarry out a polycondensation reaction under a reduced pressure of 1mmHg, whereby polyester A2 was obtained.

Acrylic Resin A1:

The acrylic resin A1 comprises 30 mol % of methyl methacrylate/30 mol %of 2-isopropenyl-2-oxazoline/10 mol % ofpolyethyleneoxide(n=10)methacrylate/30 mol % of acrylamide, with Tg(glass transition temperature) of 50° C. The acrylic resin was preparedin accordance with the procedure shown in Production Examples 1 to 3 ofKokai (Jpn. Unexamined Patent Publication) 63-37167, as follows:

302 parts of ion exchanged water were charged into a four-neck flask,and was heated to 60° C. under a nitrogen stream, followed by anaddition of 0.5 parts of ammonium persulfate and 0.2 parts of sodiumhydrogen nitrite, as polymerization initiators. Further, a mixture ofmonomers comprising 23.3 parts of methyl methacrylate, 22.6 parts of2-isopropenyl-2-oxazoline, 40.7 parts ofpolyethyleneoxide(n=10)methacrylate, and 13.3 parts of acrylamide weredropped for three hours, adjusting the temperature of the liquid to bein the range between 60 to 70° C. The temperature range was maintainedafter the completion of the dropping for two hours, to maintain thereaction under stirring. The reactants were subsequently cooled toobtain an aqueous dispersion of acrylic resin A1 containing 25% of asolid component.

Inert Particles A1:

Inert particles A1 comprise composite inorganic particles of silica andtitania, having an average particle size of 100 nm. The particles wereprepared, in accordance with the procedure shown in Production Examplesand Working Examples of Kokai (Jpn. Unexamined Patent Publication)7-2520, as follows;

140 g of methanol, 260 g of isopropanol and 100 g of aqueous ammonia (25w/t %) were charged into a glass reactor having stirring impellers andwith an inner volume of 4 litters to prepare a reaction liquid. Thereaction liquid was maintained at 40° C. with stirring. Then, into a 3litter triangular flask were charged 542 g of a silicon tetramethoxide[Si(OMe)₄, supplied by Colcoat; trade name: METHYLSILICATE 39], followedby an addition under stirring of 195 g of methanol and 28 g of 0.1 w/t %aqueous hydrochloric acid solution (35% hydrochloric acid, supplied byWako Jyunyaku Kogyo Sha, and was diluted with water to 1/1000 solution),and the mixture was stirred for about 10 minutes. Subsequently, a liquidcomprising titanium tetraisopropoxide [Ti (O-i-Pr)₄, supplied by NipponSoda KK with a trade name of A-1 (TPT)] diluted with 634 g ofisopropanol, to obtain a transparent uniform solution(co-condensationproduct of silicon tetraalkoxide and titanium tetraalkoxide). Each of1,669 g of the uniform solution and 480 g of the aqueous ammonia (25 w/t%) was simultaneously dropped into the reaction liquid for two hourssuch that the dropping speed was slow at the start and the speed wasincreased at the ending stage. After the completion of the drop, theobtained co-hydrolyzate was filtered while the organic solvent was driedat 50° C., and was dispersed in water to obtain inert particles A1having a concentration of 10% by weight and a refractive index of 1.56.

Inert Particles A2:

Acrylic filler having an average particle size of 100 nm and arefractive index of 1.50, supplied by Nippon Paint KK with a trade nameof MICROJELL E-1002

Inert Particles A3:

Acrylic filler having an average particle size of 30 nm and a refractiveindex of 1.50, supplied by Nippon Paint KK with a trade name ofMICROJELL E-2002

Inert Particles A4:

Acrylic filler having an average particle size of 200 nm and arefractive index of 1.42, supplied by Nissan Kagaku KK with a trade nameof MP-2040

Additive A1:

Carnauba wax supplied by Chukyo Yushi KK with a trade name of SELOSOL524

Wetting agent A1: polyoxyethylene (n=7) lauryl ether supplied by SanyoKasei KK with a tradename of NAROACTY-N-70

TABLE 3 Refractive index of the mixture of Coating materials highmolecular binders Coating liquid A1 1.57 Coating liquid A2 1.56 Coatingliquid A3 1.57 Coating liquid A4 1.57 Coating liquid A5 1.57

Example 11

Melted polyethylene-2,6-naphthalate ([η]=0.65 dl/g, Tg=121° C.) wasextruded from a die and was cooled in a cooling drum by a conventionalprocess to form a not-yet stretched film, followed by stretching thefilm to the longitudinal direction by 3.4-fold. Subsequently, an aqueouscoating liquid containing an 8% concentration of the coating filmcomposition (coating liquid shown in Table 2). The coated film was driedat 105° C., stretched by 3.6-fold to a crosswise direction at 140° C.,contracted by 3% to the width direction at 230° C. and heat-fixedwhereby a laminated film for optical use having a thickness of 125 μmwas obtained. The thickness of the coating film is 0.10 μm. Evaluationresults of the film are shown in Table 4.

TABLE 4 Adhesion Coat. Scratch H. Adhesive materials Res.* Haze (1)*(2)* coat (PSA) (3)* (4)* Ex. 8 Coat. liquid A1 4 ⊚ 0.007 ◯ 5 5 ◯ ◯ Ex.9 Coat. liquid A2 4 ⊚ 0.007 ◯ 5 5 ◯ ◯ Ex. 10 Coat. liquid A3 5 ⊚ 0.009 ⊚5 5 ⊚ ⊚ Ex. 11 Coat. liquid A1 4 ⊚ 0.007 ◯ 5 5 ◯ ◯ Comp. Ex. 5 Coat.liquid A4 4 Δ 0.007 ◯ 5 5 ◯ Δ Comp. Ex. 6 Coat. liquid A5 2 X 0.012 ⊚ 55 ⊚ X Ex. = Example; Comp. Ex. = Comparative Example Scratch res.* =Scratch resistance; (1)* = Surface roughness (Ra) (μm) (2)* = Frictionalcoefficient (μs); H. coat* = Hard coat; (3)* = Blocking resistance; (4)*= General evaluationExamples 12 to 20 and Comparative Examples 7 to 9

Melted polyethylene terephthalate ([η]=0.62 dl/g, Tg=78° C.) wasextruded from a die and was cooled in a cooling drum by a conventionalprocess to form a not-yet stretched film, followed by stretching thefilm to the longitudinal direction by 3.2-fold. Subsequently, an aqueouscoating liquid containing a 6% concentration of the coating materialsshown in Table 5 was applied to both surfaces of the stretched film by aroll coater. For Comparative Example 3, no coating layer was formed.

The coated film was dried at 95° C., stretched by 3.5-fold to acrosswise direction at 120° C., contracted by 3% to the width directionat 220° C. and heat-fixed whereby a laminated film for optical usehaving a thickness of 125 μm was obtained. The thickness of the coatingfilm is 0.06 μm. Evaluation results of the film are shown in Table 6.

TABLE 5 Composition (w/t %) of coating layer C.L. C.L. C.L. C.L. C.L.C.L. C.L. C.L. C.L. C.L. C.L. B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11Polyester Resin B1 80 80 80 80 80 80 Polyester Resin B2 80 80 80Polyester Resin B3 80 90 Acryl B1 10 10 10 10 10 10 10 C. linker B2 10C. linker B3 10 C. linker B4 10 Part. B1 2 2 2 2 2 Part. B2 2 2 2 2Part. B3 2 2 Add. B1 5 5 5 5 5 5 5 5 5 5 5 Wet. B1 3 3 3 3 3 3 3 3 3 3 3C.L = Coating liquid; C. linker = Cross linker Part. = Inert particles;Add. = Additive Wet. = Wetting agentComponents composing coating liquids B1 to B11 were prepared as follows:Polyester Resin B1:

The polyester resin B1 comprises, as acid components, 75 mol % of2,6-naphthalene dicarboxylic acid/20 mol % of isophthalic acid/5 mol %of 5-sodium sulfoisophthalic acid and, as glycol components, 90 mol % ofethylene glycol/10 mol % of diethylene glycol, with Tg of 80° C. and anaverage molecular weight of 12,000. The polyester resin B1 was preparedas follows:

51 parts of dimethyl 2,6-sodium dicarboxylate, 11 parts of dimethylisophthalate, 4 parts of dimethyl 5-sodium sulfoisophthalate, 31 partsof ethylene glycol and 2 parts of diethylene glycol were charged into areactor, followed by an addition of 0.05 parts of tetrabutoxy titanium.The mixture was heated to a temperature controlled to 230° C. under anitrogen atmosphere, to carry out an ester exchange reaction whiledistilling off the produced methanol. Then, the temperature of thereaction system was gradually elevated to 255° C. in a polymerizationtank provided with a stirring device having a high motor torque to carryout a polycondensation reaction under a reduced pressure of 1 mmHg,whereby polyester resin B1 having an intrinsic viscosity of 0.56 wasobtained. 25 parts of the resulted polyester was dissolved in 75 partsof tetrahydrofuran. To the resulted solution were added dropwise 75parts of water under a high speed stirring of 10,000 rotation/min, toobtain a dispersion having a milky white color. The dispersion wasdistilled under a reduced pressure of 20 mmHg to distill tetrahydrofuranoff. An aqueous dispersion of polyester resin B1 was obtained.

Polyester Resin B2:

The polyester resin B2 comprises, as acid components, 95 mol % ofterephthalic acid/5 mol % of 5-sodium sulfoisophthalic acid and, asglycol components, 90 mol % of ethylene glycol/10 mol % of diethyleneglycol, with Tg of 72° C. and an average molecular weight of 16,000. Thepolyester resin B2 was prepared as follows:

56 parts of dimethyl terephthalate, 5 parts of dimethyl 5-sodiumsulfoisophthalate, 36 parts of ethylene glycol and 3 parts of diethyleneglycol were charged into a reactor, followed by an addition of 0.05parts of tetrabutoxy titanium. The mixture was heated to a temperaturecontrolled to 230° C. under a nitrogen atmosphere, to carry out an esterexchange reaction while distilling off the produced methanol.Subsequently, the reaction system in a polymerization tank with astirring device having a high motor torque was gradually heated to 255°C. to carry out a polycondensation reaction under a reduced pressure of1 mmHg, whereby the polyester resin B2 having an intrinsic viscosity of0.57 was obtained. 25 parts of this polyester resin B2 was dissolved in75 parts of tetrahydrofuran. To the resulted solution were addeddropwise 75 parts of water under a high speed stirring of 10,000rotations/min, to obtain a dispersion having a milky white color. Thedispersion was distilled under a reduced pressure of 20 mmHg to distilloff the tetrahydrofuran. An aqueous dispersion of polyester resin B2 wasobtained.

Polyester Resin B3:

The polyester resin B3 comprises, as acid components, 75 mol % of2,6-naphthalene dicarboxylic acid/20 mol % of isophthalic acid/5 mol %of 5-sodium sulfoisophthalic acid and, as glycol components, 90 mol % ofethylene glycol/10 mol % of diethylene glycol, with Tg of 80° C. and anaverage molecular weight of 10,000. The polyester resin B3 was preparedas follows:

51 parts of dimethyl 2,6-naphthalne dicarboxylate, 11 parts of dimethylisophthalate, 4 parts of dimethyl isophthalate, 31 parts of ethyleneglycol and 2 parts of diethylene glycol were charged into a reactor,followed by an addition of 0.05 parts of tetrabutoxy titanium. Themixture was heated to a temperature controlled to 230° C. under anitrogen atmosphere, to carry out an ester exchange reaction whiledistilling off the produced methanol. Subsequently, the temperature ofthe reaction system in a polymerization tank with a stirring devicehaving a high motor torque was gradually elevated to 255° C. to carryout a polycondensation reaction under a reduced pressure of 1 mmHg,whereby the polyester resin B3 having an intrinsic viscosity of 0.57 wasobtained. 25 parts of this polyester resin B3 was dissolved in 75 partsof tetrahydrofuran. To the resulted solution were added dropwise 75parts of water under a high speed stirring of 10,000 rotations/min, toobtain a dispersion having a milky white color. The dispersion wasdistilled under a reduced pressure of 20 mmHg to distill off thetetrahydrofuran. An aqueous dispersion of polyester resin B3 wasobtained.

Acrylic Resin B1:

The acrylic resin B1 comprises 30 mol % of methyl methacrylate/3.0 mol %of 2-isopropenyl-2-oxazoline/10 mol % ofpolyethyleneoxide(n=10)methacrylate/30 mol % of acrylamide, with Tg of50° C. The acrylic resin B1 was prepared, in accordance with theprocedure shown in Production Examples 1 to 3 of Kokai (Jpn. UnexaminedPatent Publication) 63-37167, as follows:

302 parts of ion exchanged water were charged into a four-neck flask,and was heated to 60° C. under a nitrogen stream, followed by anaddition of 0.5 parts of ammonium persulfate and 0.2 parts of sodiumhydrogen nitrite, as polymerization initiators. Further, a mixture ofmonomers comprising 23.3 parts of methyl methacrylate, 22.6 parts of2-isopropenyl-2-oxazoline, 40.7 parts ofpolyethyleneoxide(n=10)methacrylate, and 13.3 parts of acrylamide wasdropped for three hours, adjusting the temperature of the liquid to bein the range between 60 to 70° C. The temperature range was maintainedafter the completion of the dropping for two hours, to maintain thereaction under stirring. The reactants were subsequently cooled toobtain an aqueous dispersion of acrylic resin B1 containing 25% of asolid component. The acrylic resin B1 contains 30 mol % of2-idoptoprnyl-2-oxazoline as a cross-linker, based on the amount of theacrylic resin B1.

Cross-Linker B2:

Methylol-melamine produced by Sanwa Chemical KK, with a trade name ofMX-035

Cross-Linker B3:

Glycerol polyglycidyl ether produced by Nagase Chemitex KK, with a tradename of DENACOL EX-313

Cross-Linker B4:

Block isocyanate produced by Daiichi Kogyo Seiyaku KK, with a trade nameof ELASTRON BN-5

Inert Particles B1:

Inert particles B2 comprise composite inorganic particles of silica andtitania, having an average particle size of 100 nm. The particles wereprepared, in accordance with the procedure shown in Production Examplesand Working Examples of Kokai (Jpn. Unexamined PatentPublication)7-2520, as follows:

140 g of methanol, 260 g of isopropanol, and 100 g of aqueous ammonia(25 w/t %) were charged into a glass reactor having stirring impellersand with an inner volume of 4 litters, to prepare a reaction liquid. Thetemperature of the reaction liquid was maintained at 40° C. withstirring. Then, into a 3 litter triangular flask were charged 542 g ofsilicon tetramethoxide[Si(OMe)₄, supplied by Colcoat; trade name:METHYLSILICATE 39], followed by an addition under stirring of 195 g ofmethanol and 28 g of 0.1 w/t % aqueous hydrochloric acid solution(35%hydrochloric acid, supplied by Wako Jyunyaku Kogyo KK, was diluted withwater to a 1/1000 solution), and the mixture was stirred for about 10minutes. Subsequently, a liquid comprising 300 g of titaniumtetraisopropoxide [Ti(O-i-Pr)₄, supplied by Nippon Soda KK with a tradename of A-1 (TPT)] diluted with 634 g of isopropanol was added, toobtain a transparent uniform solution (co-condensation product ofsilicon tetraalkoxide and titanium tetraalkoxide). Each of 1,669 g ofthe uniform solution and 480 g of the aqueous ammonia (25 w/t %) wassimultaneously dropped into the reaction liquid for two hours such thatthe dropping speed was slow at the start and the speed was increased atthe ending stage. After the completion of the drop, the obtainedco-hydrolyzate was filtered while the organic solvent was dried at 50°C., and was dispersed in water to obtain the inert particles B1 having aconcentration of 10% by weight.

Fine Particles B2:

Silica filler having an average particle size of 80 nm produced byShokubai Kasei Kogyo KK, with a trade name of CARALOID S1-80P

Fine Particles B3:

Acrylic filler having an average particle size of 80 nm produced byNippon Shokubai KK, with a trade name of MX-80W

Additive B1:

Carnauba WAX produced by Chukyo Yushi KK, with a trade name of SELOSOL524

Wetting Agent B1:

Polyoxyethylene (n=7) lauryl ether produced by Sanyo Kasei KK, with atrade name of NAROACTY N-70

TABLE 6 Surface F. Adhesion Coating roughness coeffcient to hardBlocking Heat materials Haze (Ra) (μm) (μs) coat resistance resistanceEx. 12 C.L. B1 ⊚ 0.007 ⊚ 5 ⊚ ⊚ Ex. 13 C.L. B2 ⊚ 0.007 ⊚ 5 ⊚ ◯ Ex. 14C.L. B3 ⊚ 0.007 ⊚ 5 ◯ ◯ Ex. 15 C.L. B4 ⊚ 0.007 ⊚ 5 ◯ ◯ Ex. 16 C.L. B5 ◯0.005 ◯ 5 ◯ ⊚ Ex. 17 C.L. B6 ◯ 0.005 ◯ 5 ◯ ⊚ Ex. 18 C.L. B7 ⊚ 0.007 ⊚ 5⊚ ⊚ Ex. 19 C.L. B8 ◯ 0.005 ◯ 5 ◯ ⊚ Ex. 20 C.L. B9 ◯ 0.005 ◯ 5 ◯ ⊚ Ex. 21C.L. B1 ⊚ 0.007 ⊚ 5 ⊚ ⊚ Ex. 22 C.L. B7 ⊚ 0.007 ⊚ 5 ⊚ ⊚ C. Ex. 7 C.L. B10◯ 0.005 ◯ 5 ◯ X C. Ex. 8 C.L. B11 ◯ 0.004 ◯ 5 Δ X C. Ex. 9 None ⊚ 0.002X 1 ⊚ X Ex. = Example; C. Ex. = Comparative Example C.L. = Coatingliquid

Examples 21 and 22

Melted polyethylene-2,6-naphthalate ([η]=0.65 dl/g, Tg=121° C.) wasextruded from a die and was cooled in a cooling drum by a conventionalprocess to form a not-yet stretched film, followed by stretching thefilm to the longitudinal direction by 3.4-fold. Subsequently, an aqueouscoating liquid containing a 6% concentration of the coating materialsshown in Table 5 was applied to both surfaces of the stretched film by aroll coater.

The coated film was dried at 105° C., stretched by 3.6-fold to acrosswise direction at 140° C., contracted by 3% to the width directionat 230° C. and heat-fixed whereby a laminated film for optical usehaving a thickness of 125 μm was obtained. The thickness of the coatingfilm is 0.06 μm. Evaluation results of the film are shown in Table 6.

Technical Effect of the Invention

According to the invention, there is obtained a laminated film foroptical use which is improved in uniformity, transparency, lubricity,color tone and scratch resistance, which deposits only a reduced amountof low molecular materials, and which is excellent in the adhesion to alayer adopted for various optical purposes.

1. A laminated film for optical use comprising a polyester film whichhas a lubricity layer containing globular particles in at least one sidethereof, wherein the laminated film has a thickness irregularity of 0.5to 7.0%, and wherein the polyester film contains inert particles derivedfrom catalysts and the amount of the inert particles determined by adark-field microscopy satisfies the following conditions: the number ofinert particles having a particle size of from 1 to 10 μm is 200 to20,000/mm²; and the number of inert particles having a particle size ofgreater than 10 μm is 10/mm² or less.
 2. The laminated film for opticaluse according to claim 1, wherein the inert particles are those of atleast one element selected from the group consisting of manganese,magnesium, calcium, lithium, sodium, potassium, antimony, germanium,titanium and phosphorous.
 3. The laminated film for optical useaccording to claim 1, wherein the lubricity layer contains globularinorganic particles and/or organic particles.
 4. The laminated film foroptical use according to claim 1, wherein the haze value is from 0.3 to1.5%.
 5. The laminated film for optical use according to claim 1,wherein the color*b value determined by permeated light is −0.5 to 1.5.6. The laminated film for optical use according to claim 1, wherein ablue-base dye or pigment is contained in the polyester film or lubricitylayer.
 7. The laminated film for optical use according to claim 1,wherein the polyester film is a biaxially oriented polyester film. 8.The laminated film for optical use according to claim 1, wherein thelubricity layer further contains a binder comprising a polyester resin,and wherein the difference in refractive index of the binder comprisingthe polyester resin and that of the globular particles is within 0.02.9. The laminated film for optical use according to claim 8, wherein boththe binder comprising the polyester resin and the globular particleshave refractive indexes in the range between 1.50 and 1.60.
 10. Thelaminated film for optical use according to claim 8, wherein the bindercomprising the polyester resin comprises a mixture of the polyesterresin with an acrylic resin containing oxazoline groups and polyalkyleneoxide chains.
 11. The laminated film for optical use according to claim8, wherein the lubricity layer further contains aliphatic wax.
 12. Thelaminated film for optical use according to claim 8, wherein the averageroughness (Ra) at the center line of the lubricity layer surface is from0.002 to 0.01 μm, and wherein the frictional coefficient(μs) at thelubricity layer surface is 0.8 or less.
 13. The laminated film foroptical use according to claim 8, wherein the binder comprising thepolyester resin comprises the polyester resin which has a glasstransition point of 40 to 100° C. and an intrinsic viscosity of 0.4 orgreater and less than 0.7.
 14. The laminated film for optical useaccording to claim 1, wherein the globular particles are compositeinorganic particles of silica and titania and where the average particlesize of the composite inorganic particles is from 20 to 200 nm.